Case hardening



Patented Nov. as, 1929 NETED STATES lid-20 PATENT OFFICE AUGUSTUS B. KINZEL, OF BA'YSIIDfE, NEW YORK, AS SIGNOR TO ELECTRO METALLUR- GICAL COMPANY, A CORPORATION OF WEST VIRGINIA CASE HARDENING No Drawing.

My invention relates to the case hardening of articles composed of ferrous metals.

Case hardening by heating in the presence of a nitrogenous gaseous substance, such as ammonia, is known. For successful hardening by this method it is necessary for the ferrous metal to contain an element, such as aluminum, having the ability to coact with the nitrogenous compound to produce the hardening constituent, the exact composition of which is unknown to me. The element used to develop the hardening action of the nitrogen must usually be present in critical amount, and its presence may give rise to undesirable effects, such as the non-homogeneity produced in ferrows metals under certain conditions by aluminum.

I have found that vanadium may be used with advantage to make ferrous metals amenable to hardening by nitrogenous substances. The degree of hardness attained depends on the content of vanadium, and also on the content of carbon, and is affected by the presence of other elements as will appear from the following specific examples.

A sample of steel containing 0.2% vanadium and 0.06% carbon acquired acase having a Brinell hardness of 300 when heated in ammonia at 510 C. A steel of the same carbon content but with 0.41% vanadium was hardened to 650 Brinell under the same treatment, while with 0.5% vanadium the hardness reached 900. Higher vanadium contents gave hardnesses of 900 or more.

A steel containing 0.5% vanadium but having the carbon increased to 0.3% gave a hardness of only 700, and increasing the carbon beyond this point further reduced the hardness. The effect of the carbon in reducing the hardness attained can be at least in part counteracted by the addition of such elements as chromium, manganese and silicon. These variations may perhaps be explained by the hypothesis that vanadium is only an effective hardener when present in solid solution; that in the presence of sufiicient carbon the vanadium forms a carbide which is not an effective hardener; and that the presence of elements which preferentially combine with the carbon inhibits the formation of carbides of Application filed August 20, 1927. Serial No. 214,447.

vanadium and keeps the vanadium in solid solution, where it is effective. It is my present belief that a minimum of 0.3% to 0.5% vanadium in solid solution is necessary to give a case of maximum hardness, but I do not intend to be limited to this theory nor beyond the terms of the appended claims.

The hardening is preferably carried out at temperatures between 500 C. and 580 C. At such temperatures the interior of the article treated. is practically unchanged. A temperature of 510 C. applied for a sufficient time, gives satisfactory results. Although ammonia is the preferred nitrogenizing agent, other nitrogen-containing gases or vaporizable substances may be used that similarly yield nitrogen to ferrous metals containing vanadium.

I claim:

1. An article composed of a core of ferrous metal and a surface layer harderthan said core and integral therewith, comprising a constituent that is formed by nitrogenizing an alloy containing a material which promotes the formation of a hard nitrogen containing constituent, said material being vanadium in solid solution.

2. An article composed of a core of ferrous metal and a surface layer harder than said core and integral therewith, comprising a constituent that is formed by nitrogenizing an alloy containing a material which promotes the formation of a hard nitrogen containing constituent, said material being vanadium in excess of that required to form carbides.

3. An article composed of a core of ferrous alloy and a surface layer harder than said core and integral there-with, comprising a constituent that is formed when an alloy containing a material which promotes the formation of a hard nitrogen containing constituent is nitrogenized, said material being vanadium in solid solution in excess of 3% is nitrogenized.

4. An article composed of a ferro-vanadium alloy having vanadium in solid solution in excess of about 0.3% and a hard surface layer containing nitrogen, the interior portion being softer than said layer and integral therewith.

5. An article composed of an alloy of iron, carbon vanadium and one or more carbide forming elements, the vanadium and carbide forming elements being in excess of that required to combine with the carbon so as to produce at least 0.3% vanadium in solid solution, the article having a hard surface layer containing nitrogen, the interior portion being softer than said surface layer and integral therewith.

6. The method of forming a hard surface layer which comprises adding vanadium to a ferrous material so as to form an alloy which contains about 0.3% vanadium in solid solution and then heating the alloy to temperatures not exceeding 580 (1, in the presence of a material that yields nitrogen.

7. The method of forming a hard surface layer which comprises heating a ferrous material containing more than 0.3% vanadium in solid solution to temperatures of 500 to 580 (3., in the presence of about a substance that yields nitrogen.

8. The method of forming a hard surface layer which comprises heating a ferrous material containing more than 0.3% vanadium in solid solution to temperatures of about 500 to 580 C., in the presence of ammonia.

9. The method of forming a hard surface layer which comprises heating a ferrous material containing carbon and carbide forming elements and vanadium in excess of the carbon to temperatures of about 500 to 580 C., in the presence of a substance that yields nitrogen.

10. The method of forming a hard surface layer which comprises heating a ferrous material containing carbon and carbide formnadium in solid solution in excess of about 0.3%, said alloy being substantially free from aluminum; and a hard nitrogen containing surface layer integral with said alloy core which layer consists of the alloy of said core combined with nitrogen.

In testimony whereof, I aflix my signature.

AUGUSTUS B. KINZEL.

ing elements and vanadium in excess of the carbon to temperatures of about 500 to 580 (1., in the presence of ammonia.

11. An article having an alloy core containing iron as the main constituent, vanadium in solid solution in excess of about 0.3%, aluminum less than 0.5% and at least one of the elements silicon, manganese, chromium; and a hard nitrogen-containing surface layer lntegral with said core, which layer consists of the alloy of said core combined with nitrogen.

12. An article having an alloy core containing iron as the main constituent, vanadium in solid solution in excess of about 0.3% and aluminum in amounts which do not promote the formation of. a nitrogen-containing surface layer of said core material; and a hard nitrogen-containing surface layer integral with said alloy core, said layer consisting of the alloy of said core combined with nitrogen and having a hardness corresponding to at least 900 Brinell.

An article having an alloy core contaming iron asthe main constituent and va- CERTIFICATE OF CORRECTION.

Patent No. 1,736,920. I I Granted November 26, 1929, to

aucusrus u. KINZEL.

' It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 24, claim 7, strike out the word "about" and insert the same before the numeral "500"" in line 23, same claim; and-that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in ,the Patent Office.

Signed and sealed this 21st day of April, A. o. 1931.

M. J. Moore, (Seal) Acting Commissioner of Patents. 

